The safflower plant (Carthamus tinctorius l.) is predominantly self pollinated. With self pollination, the pollen from the anthers is transferred to the stigma of the same flower, or to a flower on the same plant. To produce a hybrid from true breeding inbred male and female parents of self pollinating plants requires that the female parent be male sterile. In research test settings this can be accomplished by individual plant manipulations. Hybrids produced from different varieties of the same species (F1 hybrids) are often more vigorous than either parent, so although they cannot breed true, they are favored by the agriculturalist.
The potential of hybrid safflower has been known for many years. In 1950, Claassen (C.E. Claassen, "Natural and Controlled Crossing in Safflower, Carthamus tinctorius l.," Agronomy Journal, 42(8):381-384 (1950)) suggested using low fertility lines as female parents in a hybrid production scheme. In the intervening years many publications have used genetic analysis to indicate inheritance patterns for yield as well as yield components. Though there are differences in opinion regarding components of variation, it was commonly concluded that hybrid systems would appreciably improve the performance of safflower as reported, for example, in V.R. Rao, "Combining Ability for Yield, Percent Oil and Related Components in Safflower," Indian Journal of Genetics, 43:68-75 (1983).
Several researchers have proposed breeding systems which would enable safflower to be utilized as a hybrid crop. The first system was researched by Rubis in the 1960's. This system exploited the low fertility gene "th" as a female in a hybrid system. A summary of this program is detailed in D.D. Rubis, "Development of Hybrid Safflower," Proceedings, Third Safflower Research Conference, University of California, Davis, pages 27-32 1969). The advantages of the hybrid, as well as self-fertility problems with the female, were discussed by Urie and Zimmer (A.L. Urie and D.E. Zimmer, "The Performance of Hybrid Safflower in Competitive Yield Trials," Proceedings, Third Safflower Research Conference, University of California, Davis, pages 54-56 (1969)). This self pollination problem, along with low yields in hybrid production fields, eventually caused the program to be ended unsuccessfully.
Other hybrid programs have been pursued in recent years. A program undertaken by Cargill Seeds and Agrigenetics over the past 20 years utilizing a cytoplasmic male sterility (cms) system has produced high yielding hybrids, but no commercially available hybrids to date. With cytoplasmic inheritance, a characteristic is determined by genes in the cytoplasm (plasmagens) rather than in the nucleus. These characteristics are normally transmitted through the female gamete, which contributes most of the cytoplasm to the zygote. The male gamete only contributes to the nucleus. A summary article describing the program is reported in A.B. Hill, "Hybrid Safflower Breeding," Proceedings of the Second International Safflower Conference, Hyderabad, India, pages 169-170 (1989).
In India, safflower hybrids are available using as a female parent the genetic male sterile system (gms) based on UC148, a gms line released from University of California at Davis. (R.M. Deshmukh and N. Nimbkar, "Commercial Scale Exploitation of Hybrid Vigour in Safflower using Genetic Male Sterility System," Proceedings of the Second International Safflower Conference, Hyderabad, India, pages 163-167 (1989)). This system requires visual identification and hand roguing of male plants at anthesis, the period from flower opening to fruit set, in order to establish a pure stand of female plants. This method requires excess labor expense to ever be feasible in the USA.
Safflower is an important oilseed crop. A continuing goal of safflower breeders is to improve the crop through hybrid breeding techniques by identifying an effective male sterile plant for use in producing hybrids.